Hepatitis C virus-specific CD4+ T cell response after liver transplantation occurs early, is multispecific, compartmentalizes to the liver, and does not correlate with recurrent disease

Post-liver transplant hepatitis C virus recurrence: an unresolved thorny problem

Hepatitis C virus (HCV)-related cirrhosis represents the leading cause of liver transplantation in developed, Western and Eastern countries. Unfortunately, liver transplantation does not cure recipient HCV infection: reinfection universally occurs and disease progression is faster after liver transplant. In this review we focus on what happens throughout the peri-transplant phase and in the first 6-12 mo after transplantation: during this crucial period a completely new balance between HCV, liver graft, the recipient's immune response and anti-rejection therapy is achieved that will deeply affect subsequent outcomes. Nearly all patients show an early graft reinfection, with HCV viremia reaching and exceeding pre-transplant levels; in this setting, histological assessment is essential to differentiate recurrent hepatitis C from acute or chronic rejection; however, differentiating the two patterns remains difficult. The host immune response (mainly cellular mediated) appears to be crucial both in the control of HCV infection and in the genesis of rejection, and it is also strongly influenced by immunosuppressive treatment. At present no clear immunosuppressive strategy could be strongly recommended in HCV-positive recipients to prevent HCV recurrence, even immunotherapy appears to be ineffective. Nonetheless it seems reasonable that episodes of rejection and over-immunosuppression are more likely to enhance the risk of HCV recurrence through immunological mechanisms. Both complete prevention of rejection and optimization of immunosuppression should represent the main goals towards reducing the rate of graft HCV reinfection. In conclusion, post-transplant HCV recurrence remains an unresolved, thorny problem because many factors remain obscure and need to be better determined.

P selectins and immunological profiles in HCV and Schistosoma mansoni induced chronic liver disease

Background

Hepatitis C virus (HCV) and Schistosoma mansoni are major causes of chronic liver disease (CLD) in which immune alteration is common. Recent studies suggested that certain platelets and lymphocytes activation markers may have an impact on progression of CLD. This study aimed to evaluate the potential of platelets and lymphocytes activation molecules expression on the pathogenesis of CLD in distinct or concomitant chronic HCV and schistosomiasis mansoni infections.

Methods

The study populations were divided into group-I: patients with chronic schistosomiasis mansoni, group-II: HCV patients without cirrhosis, group-III: patients with combined liver diseases without cirrhosis, group-IV: patients with chronic HCV and liver cirrhosis and group-V: Age and sex matched healthy individuals as normal controls. All groups were subjected to full clinical evaluation, ELISA anti-HCV antibodies screening, parasitological examination for diagnosing S. mansoni and flow cytometry for lymphocyte (CD3, CD4, CD8, CD19, CD22, & CD56) and platelets activation (CD41, CD42 & CD62P (P- selectins)) markers.

Results

The platelet count was significantly decreased in HCV and/or S. mansoni patients. The total T-lymphocytes and T-helper cells were significantly reduced, while T-cytotoxics were increased. The patients possessed a significantly higher platelets activation marker; CD62P (P-selectins) and higher mean fluorescent intensity (MFI) positivity. There were considerable correlations between platelets count and both of CD62P and MFI.

Conclusion

Our Findings suggest an increased expression of certain platelets and lymphocytes activation markers in chronic HCV and S. mansoni induced CLD that may have a role in disease progression.

P selectin and T cell profiles provide verification to understand the pathogenesis of liver cirrhosis in HCV and Schistosoma mansoni infections

Hepatitis C virus (HCV) and Schistosoma mansoni are two major causes of chronic liver disease (CLD). Both immune alteration and thrombocytopenia are common complications in the majority of cirrhotic patients. The current study aimed to monitor the effect of T cell profile and platelets activation on the pathogenesis of liver cirrhosis in patients suffered from single or concomitant schistosomiasis and HCV infections. The subjects were divided into 4 groups: Group I, patients infected with schistosomiasis; Group II, patients infected with HCV; Group III, patients with combined liver diseases and Group IV: healthy individuals. All groups were subjected to full clinical evaluation as well as laboratory examination including ELISA anti-HCV antibodies screening, parasitological examination, and complete blood picture as well as flow cytometry for CD41, CD42, CD62P (P selectin), CD63, CD4 and CD8. The platelets count was significantly decreased in HCV and/or schistosoma infected patients compared to controls. The percentage of the total T-lymphocytes and T-helper was significantly reduced in all infected groups, while the percentage of T-cytotoxic was increased. The patients possessed a significantly higher percentage of the platelets activation markers than control group. There were considerable correlations between the platelets counts and P selectin and MFI. Thrombocytopenia was a common finding in patients with CLD. Patients with CLD showed increased platelets activation which may contribute to the occurrence of thrombocytopenia and play a role in the pathogenesis of CLD. Infected patient showed reduction in the cell-mediated-immunity as evidenced by low T -helper cells.

Preservation of immune function and anti-hepatitis C virus (HCV) immune responses after liver transplantation in HIV-HCV coinfected patients (ANRS-HC08 "THEVIC" trial)

BACKGROUND/AIMS

Liver transplantation (LT) in immune-suppressed human immunodeficiency virus (HIV) and hepatitis C virus (HCV) coinfected patients is feasible but raises questions regarding the severity of HCV recurrence on the liver graft and preservation of immune function. We investigated whether LT is deleterious to the immune system.

METHODS

Fourteen HIV-HCV coinfected patients (HIV viral load [VL] <50 copies/ml; median CD4 count of 276/mm(3) pretransplantation) were grafted for HCV-cirrhosis and followed over 2 years. Nine patients received anti-HCV therapy post-transplantation. HCV and HIV VLs and degree of acute and chronic hepatitis were monitored. Peripheral blood T-cell phenotypes and interferon-gamma (IFN-gamma) immune responses against opportunistic pathogens, HCV, and HIV-1 p24 were evaluated.

RESULTS

Median HCV VLs, CD4 counts, T-cell subsets, and IFN-gamma-producing T-cell frequencies against opportunistic pathogens and HIV-1 p24 did not change over time. HCV-specific T cells were observed ex vivo in two patients pretransplantation and in two others post-transplantation. HCV-specific in vitro amplification enabled the detection of HCV-specific IFN-gamma-producing responses in three further patients post-transplantation. Anti-HCV responses were observed independently of anti-HCV therapy and were undetectable in patients with severe hepatitis or liver fibrosis.

CONCLUSIONS

These results demonstrate that LT in HIV-HCV coinfected patients is not deleterious to the immune system and does not alter immune responses directed against HCV, HIV, or opportunistic pathogens.

Human liver transplantation as a model to study hepatitis C virus pathogenesis

Hepatitis C is a leading etiology of liver cancer and a leading reason for liver transplantation. Although new therapies have improved the rates of sustained response, a large proportion of patients (approximately 50%) fail to respond to antiviral treatment, thus remaining at risk for disease progression. Although chimpanzees have been used to study hepatitis C virus biology and treatments, their cost is quite high, and their use is strictly regulated; indeed, the National Institutes of Health no longer supports the breeding of chimpanzees for study. The development of hepatitis C virus therapies has been hindered by the relative paucity of small animal models for studying hepatitis C virus pathogenesis. This review presents the strengths of human liver transplantation and highlights the advances derived from this model, including insights into viral kinetics and quasispecies, viral receptor binding and entry, and innate and adaptive immunity. Moreover, consideration is given to current and emerging antiviral therapeutic approaches based on translational research results.

Molecular and cellular aspects of hepatitis C virus reinfection after liver transplantation: how the early phase impacts on outcomes

Hepatitis C virus (HCV)-related liver disease postliver transplantation is associated with an accelerated course in comparison with that observed in the nonimmunosuppressed individual. Outcomes in transplantation for this indication have, therefore, been a major area of clinical interest in the field of liver transplantation. The factors underlying the rapid progression of HCV-related liver disease posttransplantation are complex and multifactorial. Nevertheless, recent data indicate a range of parameters assessable early posttransplantation that may be useful in the prediction of outcome of transplantation for this condition. This overview, therefore, concentrates on the early events occurring postliver transplantation in the HCV-infected patient, and the implications of these recent observations for the pathogenesis of the various forms of HCV-related allograft injury.

Polyfunctional HCV-specific T-cell responses are associated with effective control of HCV replication

HCV infection has a severe course of disease in HIV/HCV co-infection and in liver transplant recipients. However, the mechanisms involved remain unclear. Here, we evaluated functional profiles of HCV-specific T-cell responses in 86 HCV mono-infected patients, 48 HIV/HCV co-infected patients and 42 liver transplant recipients. IFN-gamma and IL-2 production and ability of CD4 and CD8 T cells to proliferate were assessed after stimulation with HCV-derived peptides. We observed that HCV-specific T-cell responses were polyfunctional in HCV mono-infected patients, with presence of proliferating single IL-2-, dual IL-2/IFN-gamma and single IFN-gamma-producing CD4+ and dual IL-2/IFN-gamma and single IFN-gamma-producing CD8+ cells. In contrast, HCV-specific T-cell responses had an effector profile in HIV/HCV co-infected individuals and liver transplant recipients with absence of single IL-2-producing HCV-specific CD4+ and dual IL-2/IFN-gamma-producing CD8+ T cells. In addition, HCV-specific proliferation of CD4+ and CD8+ T cells was severely impaired in HIV/HCV co-infected patients and liver transplant recipients. Importantly, "only effector" T-cell responses were associated with significantly higher HCV viral load and more severe liver fibrosis scores. Therefore, the present results suggest that immune-based mechanisms may contribute to explain the accelerated course of HCV infection in conditions of HIV-1 co-infection and liver transplantation.

Cellular immune responses against hepatitis C virus

Cellular immune responses are typically important in recovery from acute infections, and studies of acute hepatitis C confirm that broadly directed CD4+ and CD8+ T cell responses are associated with spontaneous clearance of infection. However, a major unanswered question is what role the cellular immune response plays in progression of liver disease during chronic infection. Classic models of hepatitis C suggest that cellular immune responses promote liver injury, either by causing direct cytolysis of infected cells or by promoting inflammation. However, clinical evidence suggests that persons with cellular immune dysfunction, such as that due to with human immunodeficiency virus (HIV) infection, have more-rapid disease progression. Recent data suggest that cellular immune responses do serve to limit the progression of liver disease, even if they are ineffective at clearance of virus. There is limited information on the effect of HIV coinfection on the cellular immune response to hepatitis C virus, but further study of this issue might shed light on the pathogenesis of liver disease in both immunocompromised and nonimmunocompromised hosts.

HLA-DRB1 donor-recipient mismatch affects the outcome of hepatitis C disease recurrence after liver transplantation

BACKGROUND & AIMS

This study extends our previously reported observations that various immunological factors are associated with the occurrence of histologically proven recurrent hepatitis C. The two specific issues investigated were to confirm the associations of MHC alleles and donor/recipient mismatch with the occurrence of recurrent hepatitis C in an independent cohort of newly transplanted patients and to look for immunologic and nonimmunologic variables affecting the severity of the recurrent disease.

METHODS

Two separate cohorts of consecutive patients were studied: a look-back cohort (LC) of 120 patients and a cohort for studying the disease progression (CSDP) of 190 patients. Protocol liver biopsies were obtained at least 1, 3, 5, 7, and 10 years after liver transplantation (LT).

RESULTS

A fully mismatched donor/recipient pair at the DRB1 locus was confirmed to be associated with both the recurrence of histologic hepatitis in the LC (59% vs 23%, P = .0002) and its progression beyond stage 3 in the CSPD (71.4% vs 39.3%, P = .0003). Relevant immunologic and nonimmunologic variables were included into a multivariate Cox proportional model and three variables, namely, donor age, full HLA-DRB1 donor-recipient mismatch, and HLA B14, resulted in independent risk factors for the development of severe fibrosis.

CONCLUSION

This study provides evidence that DRB1 donor-recipient mismatch affects both the occurrence and progression of recurrent hepatitis C disease. This information is clinically relevant as it may help to better allocate organs and to recognize patients at risk for progression so that specific interventions can be implemented.

Strain-specific T-cell suppression and protective immunity in patients with chronic hepatitis C virus infection

Hepatitis C virus (HCV) frequently persists with an apparently ineffective antiviral T-cell response. We hypothesized that some patients may be exposed to multiple HCV subtypes and that strain-specific T cells could contribute to the viral dynamics in this setting. To test this hypothesis, CD4 T-cell responses to three genotype 1a-derived HCV antigens and HCV antibody serotype were examined in chronically HCV infected (genotypes 1a, 1b, 2, 3, and 4) and spontaneously HCV recovered subjects. Consistent with multiple HCV exposure, 63% of patients infected with genotypes 2 to 4 (genotypes 2-4) and 36% of those infected with genotype 1b displayed CD4 T-cell responses to 1a-derived HCV antigens, while 29% of genotype 2-4-infected patients showed serotype responses to genotype 1. Detection of 1a-specific T cells in patients without active 1a infection suggested prior self-limited 1a infection with T-cell-mediated protection from 1a but not from non-1a viruses. Remarkably, CD4 T-cell responses to 1a-derived HCV antigens were weakest in patients with homologous 1a infection and greater in non-1a-infected patients: proportions of patients responding were 19% (1a), 36% (1b), and 63% (2-4) (P = 0.0006). Increased 1a-specific CD4 T-cell responsiveness in non-1a-infected patients was not due to increased immunogenicity or cross-reactivity of non-1a viruses but directly related to sequence divergence. We conclude that the T-cell response to the circulating virus is either suppressed or not induced in a strain-specific manner in chronically HCV infected patients and that, despite their ability to clear one HCV strain, patients may be reinfected with a heterologous strain that can then persist. These findings provide new insights into host-virus interactions in HCV infection that have implications for vaccine development.

Reconstitution of hepatitis C virus-specific T-cellmediated immunity after liver transplantation

Hepatitis C virus (HCV)-related liver failure is the leading indication for liver transplantation worldwide. After transplantation, virological recurrence is the rule, but the spectrum of histological injury is wide, ranging from the development of allograft cirrhosis within a few years to minimal hepatitis despite long-term follow-up. The immunological correlates of this variable natural history are poorly understood. Here, we studied the kinetics of the cellular immune responses, viral replication, and allograft histology in 24 patients who had undergone liver transplantation for HCV-related liver failure. Using direct ex vivo methodologies (i.e., interferon-gamma ELISPOT and major histocompatibility complex class I-peptide tetrameric complexes), we found that patients who experienced viral eradication after antiviral therapy showed restoration of HCV-specific T-cell responses, whereas patients with progressive HCV recurrence that failed to respond to therapy showed declining frequencies of these viral-specific effector cells. The cytotoxic T lymphocytes that peripherally reconstituted after transplantation were clonotypically identical to those present within the recipient explant liver, defined at the level of the T-cell receptor beta chain (one epitope/one clone). Moreover, the subset of patients who spontaneously demonstrated minimal histologic recurrence had more vigorous CD4+ T-cell responses in the first 3 months, particularly targeting nonstructural proteins. We provide evidence that T-cell responses emerge after liver transplantation, and their presence correlates with improved histological and clinical outcomes. In conclusion, these results may help identify patients more likely to develop severe HCV recurrence and therefore benefit from current antiviral therapy, as well as provide a rationale for the future use of novel immunotherapeutic approaches. Supplementary material for this article can be found on the HEPATOLOGY website (http://interscience. wiley.com/jpages/0270-9139/suppmat/index.html).

Cell-Mediated Immunity and the Outcome of Hepatitis C Virus Infection

The hepatitis C virus (HCV) infects approximately three percent of the world's population. Some individuals resolve the infection spontaneously, but the majority develop persistent viremia that often causes progressive liver disease. There is an emerging consensus that cellular immune responses are essential for spontaneous resolution of acute hepatitis C and long-term protection from persistent infection. This review focuses on the recent advances in understanding mechanisms of protective immunity and why they fail in most infected individuals. The distinct yet complementary role of CD4+ and CD8+ T lymphocytes in this process is highlighted.

Immune responses in hepatitis C: is virus or host the problem?

PURPOSE OF REVIEW

Hepatitis C virus is an RNA virus that usually establishes persistent infection in its host. As an important cause of cirrhosis and hepatocellular carcinoma worldwide, hepatitis C is a growing public health concern. Despite recent advances in therapy, most people infected with the virus can expect lifelong infection. In the minority of those exposed and who spontaneously clear virus, a robust hepatitis C virus-specific T cell response of T helper 1 type correlates with resolution. The longevity of this response in the recovered state and the potential for hepatitis C virus-specific T cells to protect against future infection are critical parameters for vaccine design.

RECENT FINDINGS

The literature of the past year dissected components of protective immunity to hepatitis C and emphasized the importance of the CD4 helper response in both the expansion and maintenance of hepatitis C virus-specific CD8(+) T cells. Other important studies examined how the virus interacts with immune cells to subvert both innate and adaptive immune responses in acute and chronic infection.

SUMMARY

Defining the essential components of protective immunity against a highly mutable virus like hepatitis C underpins successful vaccine design. By understanding viral and host factors which influence hepatitis C virus-specific T cell maintenance and function, we are better equipped to devise immunomodulatory therapies and vaccines which induce robust and lasting immunity.

Impact of immunosuppression on immunopathogenesis of liver damage in hepatitis C virus-infected recipients following liver transplantation

1. Hepatitis C virus (HCV) infection in the allograft occurs in the setting of greater viral burdens than in patients pretransplantation. 2. Viral burden is increased by such immunosuppressive therapies as corticosteroids and interleukin-2 receptor antibodies. 3. Cholestatic HCV infection occurs in the setting of very high viral load and is almost certainly induced by overimmunosuppression. It is managed best by rapid reduction in levels of immunosuppression. 4. The more common chronic hepatitic HCV disease seems to behave at the molecular/cellular level in a fashion similar to the nontransplantation setting with activation of T helper subtype 1 inflammatory, profibrotic, and proapoptotic pathways. The role of immunosuppression in the acceleration of this disease is unclear, and rapid reduction in immunosuppressive doses may be detrimental. 5. Changes to definitions of types of HCV disease recurrence, disease severity, and acute allograft rejection in the presence of HCV infection are required to improve understanding of the pathogenesis.

Sequence variation in the hypervariable region 1 of hepatitis C virus and posttransplantation recurrent hepatitis

Hepatitis C virus (HCV) shows remarkable genetic variation in both populations and individuals, in whom it circulates as quasispecies (QS). Sequence variation within an infected host has adaptive significance and reflects the modes and intensity of selection mechanisms operating on the virus. We investigated the sequence diversity of hypervariable region 1 of HCV in liver transplant recipients and correlated it with the recurrence of hepatitis. Twenty-six patients were considered during a 2-year period; all had graft reinfection, and 14 patients developed hepatitis recurrence. Cloned sequences were obtained from sera collected before or within 1 month after orthotopic liver transplantation (OLT) and at 3 and 24 months thereafter. Sequence diversity within single sera and over consecutive samples was analyzed quantitatively by matrix comparison and phylogenetic analysis. Propagation of viral QS in the graft was markedly dependent on individual factors. Viral QS in post-OLT sera were less complex and evolved slower compared with immunocompetent subjects with chronic hepatitis. Sequence variation was greater during the first 3 months post-OLT than during the remaining period. Genetic diversity within single samples was not related to hepatitis recurrence or other clinical features. Conversely, sequence diversity over consecutive samples was reduced in patients who experienced hepatitis recurrence, in particular, in those infected with genotype 1b and with an HLA-DR mismatched graft. Selection of viral sequences was markedly impaired in liver transplant recipients and tended to be greater early after OLT. Reduced sequence turnover correlated negatively with the outcome of graft reinfection.

Antiviral treatment of recurrent hepatitis C virus (HCV) infection after liver transplantation: association of a strong, multispecific, and long-lasting CD4+ T cell response with HCV-elimination

BACKGROUND/AIMS

Patients with recurrent hepatitis C virus (HCV)-infection after liver transplantation (OLTx) could develop an early, multispecific, preferentially intrahepatic CD4+ T cell response. We asked now whether there is a correlation between the HCV-specific CD4+ T cell response and treatment outcome in patients who receive interferon (IFN)-alpha/ribavirin.

METHODS

Liver- and blood-derived T cell lines of 20 patients were studied in parallel before, under, at the end and after antiviral treatment. Virus-specific IFN-gamma production at a single cell level to HCV-proteins (core, non-structural protein (NS)3/4, NS5) was determined by enzyme-linked immunospot assay.

RESULTS

In 6/7 non-responders a weak HCV-specific CD4+ T cell response was detectable. All six sustained responders developed a strong, at NS3/4 and NS5 directed and long-lasting CD4+ T cell response which was mainly detected in peripheral blood mononuclear cells. This reaction was significantly stronger: (1) in the responders than in the non-responders; and (2) within the responders at the end of treatment than before (P<0.03). Seven transient-responders showed a weak and/or transient HCV-specific CD4+ T cell response.

CONCLUSIONS

In patients with recurrent HCV-infection after OLTx, who receive antiviral treatment, a strong, at NS3/4 and NS5 directed and long-lasting CD4+ T cell response is associated with HCV-elimination whereas no or a weak/transient response is associated with treatment failure.

Influence of ethnicity in the outcome of hepatitis C virus infection and cellular immune response

This study was performed to examine the immunologic basis for the apparent ethnic difference in clinical outcome of hepatitis C virus (HCV) infection between African Americans (AA) and Caucasian Americans (CA). To this end, we recruited 99 chronically HCV-infected and 31 spontaneously HCV-cleared subjects for clinical, virologic, and immunologic analysis. In particular, CD4-proliferative T-cell response to genotype 1-derived HCV antigens (core, NS3-NS5) was examined in 82 patients chronically infected with genotype 1 (54 AA, 28 CA) and in all HCV-cleared subjects (14 AA, 17 CA). HCV-specific Th1 response also was examined in 52 chronic and 13 recovered subjects. Our results showed that HCV clearance was associated with a vigorous HCV-specific Th1 response irrespective of ethnic origin. Although the HCV-specific CD4 T-cell response clearly was weaker during chronic infection, AA ethnicity in this setting was associated with a significantly greater CD4-proliferative T-cell response to HCV, particularly to the nonstructural antigens (22% AA vs. 0% CA, P =.007) as well as better clinical parameters of liver disease. Interestingly, most HCV-specific CD4 T-cell proliferative responses in AA patients were unaccompanied by concurrent interferon gamma (IFN-gamma) production, suggesting a dysregulated virus-specific, CD4 T-cell effector function during chronic HCV infection. In conclusion, our results suggest that host ethnicity does influence the clinical outcome and antiviral T-cell response during HCV infection. AA ethnicity is associated with a more robust antiviral CD4 T-cell response than CA ethnicity, although these T cells are limited in direct virus or disease control due to their dysfunctional nature.

Hepatitis C virus in the human liver transplantation model

Hepatitis C virus-related liver failure is the single leading indication for liver transplantation, and the study of HCV in the transplant setting has enhanced the understanding of the natural history of disease and putative mechanisms by which HCV causes liver injury. In a subset of patients, allograft cirrhosis develops within a few years after transplantation, and recent findings suggest these individuals are immunologically impaired compared with individuals with mild HCV recurrence at long-term follow-up. Fig. 9 shows a conceptual paradigm of mechanisms potentially involved in shaping HCV outcome after transplantation. It is possible that relative antiviral control by innate and adaptive immune responses (to maintain HCV replication below a certain threshold) prevents direct cytopathic injury and induction of oxidative stress and apoptosis of cells. Additional phenomena that may contribute to induction of apoptosis (eg, genetic polymorphisms within the donor organ. CMV coinfection, and ischemic-preservation injury) may augment the initial cascade of liver injury. Recruitment to the allograft of nonspecific cells may decrease viral replication by way of noncytolytic mechanisms or augment viral replication (eg, Th2 phenotype) and direct cytopathic injury. The immune response is likely insufficiently vigorous to keep viral replication under control, but may maintain chronic liver injury. The liver transplant model is unique in that distinct phenotypic outcomes can be observed over a short period of time. A consideration of the temporal evolution of different mechanisms is also important, because mechanisms that initially predominate may become less important over time, and conversely, as suggested with the inverse correlation between viral load at 5 years and allograft fibrosis, new immune responses may emerge that modify the host-virus interaction. Prospective characterization of the immunoregulatory and virologic mechanisms involved in the liver transplantation model hopefully will help unravel the causal basis of reported associations, lead to the development of highly specific therapeutic strategies, and ultimately diminish the rate of graft loss from recurrent disease.

Immunopathogenesis of hepatitis C virus infection

HCV infection becomes persistent in many patients who are otherwise immune competent. There is increasing support for potential contribution of innate immune response and viral interference with its components to the subsequent outcome. As for the adaptive immune response, humoral immunity may be largely ineffective despite evidence for neutralizing antibody response directed to the E2 HVR region, perhaps due to rapid selection of antibody escape variants. Cellular immune response does seem to play a role in the virologic outcome during acute infection based on strong association of a sustained vigorous and multispecific antiviral CD4 and CD8 T cell response with HCV clearance during acute infection. Following clearance, vigorous CD4 T cell response to HCV is maintained for many years, whereas the memory CD8 T cell response may be maintained with variable efficiency. If unable to clear the virus quickly, the T cell response (particularly if focused) may also select for T cell escape variants that are poorly recognized by the circulating T cells or even actively inactivate them through T cell antagonism. In established chronic infection. HCV-specific T cell response is quantitatively weak, providing only minimal selection pressure for further escape mutation. Although earlier studies using conventional in vitro techniques suggest that this low-frequency T cell response may help control the virus and liver disease progression, the role and nature of these apparently defective T cells in the outcome of chronic HCV infection remains to be fully determined. In summary, much progress has been made in the field of HCV immune pathogenesis since the initial identification of HCV. Although more work is needed to define the mechanism of HCV persistence and liver cell injury, there is considerable hope as well as challenge for potential development of vaccine and immunotherapy for HCV infection (see article by Drs. Inchaupsé and Feinstone). A better understanding of the relevant host and viral factors for clinical and virologic outcome, and the mechanism of selective immune defect against HCV, will be invaluable in our ability to treat the many patients infected with HCV.

Mycophenolate mofetil in combination with recombinant interferon alfa-2a in interferon-nonresponder patients with chronic hepatitis C

BACKGROUND/AIMS

Since ribavirin was able to improve the antiviral efficacy of interferon alfa in patients with chronic hepatitis C, several other adjuncts have been studied. It has been shown that mycophenolate mofetil (MMF) is a more potent inhibitor of the inosine 5'-monophosphate-dehydrogenase (IMPDH) than ribavirin. The present study is a pilot study evaluating the efficacy and safety of combination therapy with interferon alfa-2a and MMF in interferon alfa nonresponder patients.

METHODS

Thirty-eight adult patients with chronic hepatitis C who did not respond to a previous interferon alfa monotherapy were enrolled to receive 6 million units of interferon alfa-2a tiw in combination with MMF (1 week 500 mg/day, 1 week 1000 mg/day, 22 weeks 2000 mg/day).

RESULTS

An interim analysis of 29 patients after 12 weeks of therapy showed that only one patient had negative hepatitis C virus-RNA at this time point. There was no significant reduction of the viral load during therapy. Due to inefficacy the study was discontinued.

CONCLUSIONS

Combination therapy of interferon alfa-2a and MMF is ineffective in improving virological response rates in nonresponder patients with chronic hepatitis C. These data suggest that inhibition of the IMPDH seems not to be the major mechanism of ribavirin in enhancing the antiviral effect of interferon alfa in chronic hepatitis C.

Pathogenesis of hepatitis C virus recurrence in the liver allograft

1. Hepatitis C virus (HCV) infection in the allograft occurs in the setting of greater viral burden than in nontransplantation patients. 2. Infection of the allograft occurs early (within days and possibly during the intraoperative reperfusion phase). 3. Viral burden plateaus at 1 month posttransplantation and (in the absence of cholestatic HCV) peaks at the time of acute hepatitis (1 to 4 months). 4. Acute hepatitis is associated with immune cell infiltration and hepatocyte apoptosis. 5. Cholestatic HCV seems to be a disease of direct HCV cytopathic injury in the setting of extreme virus levels, an intrahepatic T helper subtype 2 cell (T(H)2)-like response, and lack of a specific HCV-directed response. 6. Chronic hepatitic HCV seems to behave at the molecular and/or cellular level in a similar fashion to the nontransplantation setting, with activation of T(H)1 inflammatory, profibrotic, and proapoptotic pathways. This process operates at a greater viral burden than pretransplantation and leads to more progressive disease. 7. More studies are required to examine and distinguish allograft rejection in the setting of HCV infection from HCV infection alone.

Hepatitis C in the liver transplant recipient: current understanding and treatment

Hepatitis C virus (HCV)-related liver disease is the leading indication for orthotopic liver transplantation worldwide. Recurrent HCV infection as defined by viremia after transplantation is nearly universal, with histologic evidence of recurrent hepatitis present in the majority. Although short-term survival appears to be similar to that in other causes of liver failure, it has recently been demonstrated that approximately 20-30% of HCV-positive patients develop allograft cirrhosis by 5 years. Therefore, it is possible to define disease outcomes within a relatively short period of follow-up. Identification of patients who are likely to develop progressive HCV-related allograft injury is important to optimize results of current antiviral therapy.

A longitudinal analysis of T-cell epitope-coding regions of hepatitis C virus after liver transplantation

BACKGROUND

Hepatitis C virus (HCV)-related liver failure is the single leading indication for orthotopic liver transplantation (OLT) worldwide. The mechanisms that underlie the observed differences in natural history of HCV recurrence remain poorly understood. We have previously demonstrated that differential T-cell responses correlate with histologic severity after OLT. We hypothesized that amino acid substitutions within critical T-cell epitopes could lead to increased severity of HCV disease.

METHODS

We determined the peptide sequences from sequential serum-derived viral RNA by reverse transcription and direct polymerase chain reaction sequence analysis from 32 HCV genotype 1-infected patients with well-characterized outcomes after liver transplantation. Serum samples were analyzed for HCV sequence the day of OLT and at least one time point post-OLT. To construct evolutionary relationships among the different patient samples, phylogenetic analyses of core and NS3 sequences were performed using a matrix fed into a neighbor-joining tree algorithm.

RESULTS

The phylogenetic analyses revealed remarkable conservation within a given individual and no significant differences when comparing patients with severe versus mild recurrence. Accordingly, the synonymous mutation rate was consistently greater than the nonsynonymous substitution rate. The nine epitopic regions analyzed were also preserved so that, with the exception of one patient with mild recurrence, none of the patients demonstrated a shift in viral peptide sequence.

CONCLUSIONS

HCV core and NS3 viral peptide sequences are identical before and after OLT in most patients, suggesting that the prevalent sequence is preserved in most cases, and viral variants are competent to establish infection after OLT. Although these results do not support viral mutation as a dominant pathogenic mechanism after OLT, other viral regions need to be analyzed.

Immunopathogenesis of hepatitis C virus in the immunosuppressed host

The prevalence of chronic hepatitis C virus (HCV) infection among various groups of immunosuppressed patients is high. These groups include patients co-infected with human immunodeficiency virus (HIV), recipients of organ transplants, and those with hypogammaglobulinemia. The liver disease in the immunosuppressed host is typically severe with an unusually rapid progression to cirrhosis. This is somewhat paradoxical, as the classical model for HCV-induced liver disease assumes that cell-mediated immune responses induce liver injury. It is likely that a combination of viral-related factors and host-related factors plays a role in this accelerated natural history of HCV. Data are accumulating in immunocompromised hosts that address the immunopathogenesis of liver injury, although there are still fundamental gaps in our understanding of this process. In this review, we will focus on our current understanding of the mechanisms of liver injury and how it relates to the accelerated liver disease progression in immunocompromised hosts.

Immunity to hepatitis C virus: stunned but not defeated

Hepatitis C virus (HCV) readily causes a persistent infection, although some individuals spontaneously control infection. 'Successful' immune responses appear to be multi-specific and sustained-including a major role for CD4(+)T cells. Some antiviral CD8(+)T cells show reduced capacity to secrete antiviral cytokines either temporarily ('stunning') or in the long term ('stunting'). The co-ordination of multiple immune effector functions may be required to gain control of HCV.